Method for determining the exhaust pressure of a turbocharged internal combustion engine

Abstract

A method for determining the exhaust pressure (P_r) of a turbocharged internal combustion engine, including a solenoid by-pass valve for the exhaust gas, characterized in that an exhaust pressure (P_i) is determined as a function of the inlet air flow to the engine, (A_r), the engine speed (R_r) and the degree of opening of the solenoid exhaust by-pass valve (T_r), by interpolation from a reference map having exhaust gas pressure values (P_c) for given inlet air flow values (A_c), the engine speed (R_c) and the degree of opening of the solenoid exhaust by-pass valve (T_c), and the exhaust pressure determined by the interpolation (P_i) is corrected as a function of ambient pressure values (P_a, P_o).

Description

The invention relates to a method of determining the exhaust pressure of a turbocharged internal combustion engine, and to a method of regulating such an engine.

The exhaust pressure is an important piece of data for regulating a turbocharged internal combustion engine in order to take account of the back pressures. In the prior art, this pressure is determined by means of a pressure sensor arranged in the exhaust manifold. However, given its position, the sensor must be able to withstand high temperatures, thereby making its manufacture more complex and its cost more substantial.

A problem that the present invention aims to solve is that of determining the exhaust pressure without using a sensor in the exhaust manifold.

According to the invention, the exhaust pressure is determined, as a function of the engine intake air flow rate, of the engine speed and of the degree of opening of the solenoid valve used for bypassing the exhaust gases (commonly referred to as a wastegate), by an interpolation from a reference map comprising exhaust pressure values for defined values of the intake air flow rate, of the engine speed and of the degree of wastegate opening.

This exhaust pressure determined by interpolation is then corrected, as a function of the ambient pressure prevailing during the determination of the exhaust pressure and of the ambient pressure prevailing during the production of the map, according to the formula which follows.

Thus, according to the invention, the pressure sensor in the exhaust is eliminated, the pressure being determined from an interpolation performed by a computer using a reference map established on a test bench.

Other particular features and advantages of the present invention will become apparent from the detailed description of the example illustrated in the appended figures.

FIG. 1 is a schematic representation of a map representing the exhaust pressure values as a function of intake air flow rate values, engine speed values and wastegate control values;

FIG. 2 is a diagram illustrating the process of determining the exhaust pressure by using a map as illustrated in FIG. 1, followed by a correction which makes it possible to take account of the ambient pressure;

FIG. 3 is a schematic representation illustrating the determination of the corrective factor used for correcting the value of the pressure determined by interpolation; and

FIG. 4 is a graph comparing the exhaust pressure measured and the exhaust pressure obtained according to the present invention.

According to the invention, a reference map is established for a given type of engine (internal combustion engine). This map is produced from an engine on a test bench. The map is obtained by carrying out a number of exhaust pressure measurements P_c, each exhaust measurement being conducted for a defined value of the intake air flow rate A_c, of the engine speed R_c and of the degree of wastegate opening T_c. The degree of opening is between 0 and 100% and it represents the position of greater or lesser opening of the wastegate.

In the present example, the degree of wastegate opening T_c is represented by the value of the wastegate control.

In the map illustrated in FIG. 1, the air flow rate A_c is expressed in mg for each piston stroke, the engine speed R_c is expressed in revolutions per minute, the value of the wastegate control T_c is expressed as a percentage of the duty cycle of the control (ratio of the duration for which the wastegate is in the opening position in a cycle to the duration of the cycle), and the exhaust pressure P_c is expressed in mbar.

In FIG. 1, the x axis represents the intake air flow rate A_c, the y axis represents the engine speed R_c, each layer represents a value of the wastegate control T_c, and the z axis represents the exhaust pressure P_c.

During the use of the given type of engine, the exhaust pressure P_i is determined, as a function of the actual engine intake air flow rate A_r, of the actual engine speed R_r and of the actual value of the wastegate control T_r, by an interpolation from the reference map produced for this type of engine. Preferably, the interpolation used is a linear interpolation.

Of course, to ensure that this interpolation gives a correct value, the number of intake air flow rate values A_c, engine speed values R_c and wastegate control values T_c required to establish the map must be sufficient. Thus, for the wastegate control T_c, three or four values (hence three or four layers) are sufficient to obtain a reliable linear interpolation.

The value of the exhaust pressure P_i thus determined by interpolation can then be used to regulate the turbocharged engine.

A correction can be applied to the exhaust pressure determined by the interpolation P_i in order to take account of the ambient pressure P_a, more precisely to take account of the difference between the ambient pressure prevailing during the production of the map P_o and that prevailing during the use of the engine P_a.

The exhaust pressure P_i can thus be corrected according to the formula which follows:

$P_r=P_i\left(P_i\left(\frac{1-\frac{P_a}{P_o}}{K-P_a}\right)+\frac{\frac{K{P}_a}{P_o}-P_a}{K-P_a}\right)$
in which K is a corrective factor, P_r is the corrected exhaust pressure, P_i is the exhaust pressure determined by the interpolation, P_o is the ambient pressure prevailing during the production of the map, and P_a is the ambient pressure prevailing during the determination of the exhaust pressure, P_o, P_a and K being expressed in mbar.

The corrective factor K, specific to one type of engine, is determined on a test bench by calibrating measurements at different ambient pressures. As can be seen from FIG. 3, for each atmospheric pressure the ratio of the actual exhaust pressure P (measured by a sensor) to the exhaust pressure determined by the interpolation P_i is represented as a function of the exhaust pressure determined by the interpolation P_i. This representation is a straight line whose slope and ordinate at the origin depend on the atmospheric pressure at which the measurements are carried out. The corrective factor K is the point of intersection of the various straight lines representing the various tests carried out at different atmospheric pressures.

In FIG. 3, the six atmospheric pressures at which the measurements were carried out are 600, 700, 800, 900, 1000 and 1100 mbar.

FIG. 2 illustrates the method of determining the exhaust pressure P_r with, in a first step, the determination of the exhaust pressure by interpolation P_i from the pre-established reference map as a function of the actual engine intake airflow rate A_r, of the actual engine speed R_r and of the actual value of the wastegate control T_r, and, in a second step, the determination of the corrected exhaust pressure P_r from the predetermined corrective factor K as a function of the interpolated exhaust pressure P_i, of the ambient pressure prevailing during the production of the map P_o, and of the actual ambient pressure P_a.

As can be seen from FIG. 4, the values of the corrected exhaust pressure P_r agree with the measured exhaust pressure values P_m (measured by a sensor).

It would be possible to apply other corrections in order to further improve the reliability of the determination of the exhaust pressure by computation. These other corrective factors may be the air/fuel ratio of the admitted mixture, the ignition advance delay and the injection interruptions.

It would be possible to produce a map using the intake airflow A_c expressed in kg/h (along the x axis), the wastegate control T_c expressed as a percentage of the duty ratio (along the y axis), each layer thus representing a value of the engine speed, and the z axis representing the exhaust pressure P_i. However, the use of such units gives rise to a more complex calibration process.

It would also be possible, to ensure that the wastegate control is even more representative of the actual position of this wastegate, to use the applied control less the adaptation corrections so as to take the drifts and the aging of the wastegate correctly into account. This prevents any drift of the modeled exhaust pressure. The adaptation of the control thus makes it possible to maintain a constant position, which remains represented in the map by the non-corrected control.

It would also be possible to use the actual position of the wastegate instead of the control of this wastegate. However, it is then necessary to use a sensor to determine this position.

Claims

1. A method of determining the exhaust pressure (P_r) of a turbocharged internal combustion engine comprising a wastegate, characterized in that

an exhaust pressure (P_i) is determined, as a function of the engine intake air flow rate (A_r), of the engine speed (R_r) and of the degree of wastegate opening (T_r), by an interpolation from a reference map comprising exhaust pressure values (P_c) for defined values of the intake air flow rate (A_c), of the engine speed (R_c) and of the degree of wastegate opening (T_c),

the exhaust pressure determined by the interpolation (P_i) is corrected, as a function of the ambient pressure prevailing during the determination of the exhaust pressure (P_a) and of the ambient pressure prevailing during the production of the map (P_o), according to the formula which follows:

2. The method as claimed in claim 1, characterized in that the interpolation used is a linear interpolation.

3. The method as claimed in claim 1, characterized in that the degree of wastegate opening (T_c) is represented by the actual position of the wastegate measured by a sensor.

4. The method as claimed in claim 1, characterized in that the degree of wastegate opening (T_c) is represented by the value of the wastegate control.

5. The method as claimed in claim 4, characterized in that the wastegate control is the applied control less the adaptation corrections.

6. A method of regulating a turbocharged internal combustion engine as a function of the exhaust pressure, characterized in that the exhaust pressure is determined as claimed in claim 1.

7. The method as claimed in claim 2, characterized in that the degree of wastegate opening (T_c) is represented by the actual position of the wastegate measured by a sensor.

8. The method as claimed in claim 2, characterized in that the degree of wastegate opening (T_c) is represented by the value of the wastegate control.

9. The method as claimed in claim 3, characterized in that the degree of wastegate opening (T_c) is represented by the value of the wastegate control.

10. A method of regulating a turbocharged internal combustion engine as a function of the exhaust pressure, characterized in that the exhaust pressure is determined as claimed in claim 2.

11. A method of regulating a turbocharged internal combustion engine as a function of the exhaust pressure, characterized in that the exhaust pressure is determined as claimed in claim 3.

12. A method of regulating a turbocharged internal combustion engine as a function of the exhaust pressure, characterized in that the exhaust pressure is determined as claimed in claim 4.

13. A method of regulating a turbocharged internal combustion engine as a function of the exhaust pressure, characterized in that the exhaust pressure is determined as claimed in claim 5.